Referring to FIG. 13 and FIG. 14, the upper diagram of FIG. 13 shows the electromagnetic torque (which is direct proportional to back-EMF) of an existing single phase permanent magnet motor during one electric period, where the horizontal axis represents time, the vertical axis represents the amplitude of electromagnetic torque. The lower diagram of FIG. 13 is a curve diagram showing the changing of the cogging torque of the existing single phase permanent magnet motor during one electric period, where the horizontal axis represents time, and the vertical axis represents cogging torque. FIG. 14 illustrates the motor output torque that is synthesized from the electromagnetic torque and the cogging torque of FIG. 13. Because the torque fluctuation rate=(maximal torque−minimum torque)/mean torque, as can be seen from FIG. 14, the fluctuation rate of the output torque of the existing single phase permanent magnet motor=(47−0)/20=235%. In other existing motors, the fluctuation rate of the output torque of the single phase motors is at least greater than 100%. As a result, the existing single phase motor during operation generates a large torque fluctuation, which causes obvious motor vibration and large noise.